This invention relates to a heavy duty blow molded wheel adaptable for many purposes but described in this application for particular use with a roll-out waste container of the type commonly used by waste haulers and municipalities for "street-side" waste collection.
One-piece molded plastic wheels are known in the prior art. However, prior art wheels are designed to resemble older-type pneumatic or semi-pneumatic wheels. Generally, this means that the side wall and tread portions of the plastic wheel are designed to resemble the rubber tire portion of a pneumatic or semi-pneumatic wheel, included a rounded tread area and a rounded, relatively thick width side wall.
There are, of course, reasons why a pneumatic tire has a rounded tread and side wall cross-section. Since the tire is filled with pressurized air, the tire will naturally want to assume a rounded cross-section since the air is pressing with equal force on all interior parts of the tire. Furthermore, since a pneumatic tire is designed to compress under weight and to absorb and cushion irregularities in the rolling surface, a relatively thick width side wall is required so that the tire will not be compressed to the point where the tread bottoms out on the wheel rim under heavy impact or weight loads. In other words, the side wall needs to be relatively thick and compressible to take full advantage of the benefits offered by pneumatic and semi-pneumatic rubber tires.
Likewise, the axle bore of a pneumatic or semi-pneumatic tire generally comprises a steel sleeve or similar structure inserted into the wheel and, in any event, is cushioned from extreme shock by the highly compressible nature of the tire itself.
These considerations to not apply in the use of plastic wheels. Plastic wheels are relatively stiff and brittle in comparison to rubber tires. Of course, plastic wheels are not pneumatic. They are generally used in situations where loads are not great, and on relatively even surfaces where it is not necessary to cushion impact on the wheel, for example on roll-out waste containers.
However, roll-out waste containers are becoming larger and are designed to carry much heavier loads. For these reasons, conventionally designed plastic wheels are now subject to crushing due to heavy loads placed on them. This crushing usually occurs in the side-wall area and/or in the area of the axle bore, both of which have a relatively thin cross-sectional dimensions in prior art wheels. Since the side wall area is generally perpendicular, or normal, to the direction of load application, the side walls are caused to bulge out under load and the axle bore will crush or wallow out. The relatively brittle plastic is not designed to flex to any substantial degree, and for this reason the side wall and the axle bore area breaks down, damaging the wheel and eventually requiring replacement. The axle bore in prior art wheels has a relatively open, unsupported core structure which is subject to stress and eventual wear and breakage. The axle bore area is generally supported only adjacent its opposite ends, with a void between the opposing side walls of the wheel around the bore area.
Of course, the cross-sectional thickness of the core area of the axle bore can be made progressively greater to withstand heavier loads. However, this increases the expense and weight of the wheel.
It has been discovered that a wheel which will withstand heavy-duty loads without damage can be made using no more or even less material by supporting the axle bore with integrally formed, adjacent core structures within the radius of the wheel itself.